DN498519170

Subject: Re: Tcl "expr" command change suggestion - DN [1]

"Richard.Suchenwirth" <Richard.Suchenwirth@kst.siemens.de> - 08 Jul 1999 - comp.lang.tcl

 Costas Menico wrote:
 > A command in Tcl is enclosed in [ ].
 Sometimes, yes. If its return value shall be used in another command.

 > It is not enclosed in { }.
 What about "foreach i {red green blue} {puts hello,$i}"

 So the requirement is  that you would still use the command brackets.
 > E.g.   [expr 1 + 1]  can be [1 + 1]

 A command has a name and a sequence of arguments. In your example,
 command "1" (legal name) would be called with arguments "+ 1".
 As they used to say before Tcl 8.0, "everything is a string" - depends
 what you do with it. The few syntax rules in Tcl(n) are enough, and good
 enough, for me, and a number of other folks. Still, in Tcl you're free
 to do many things you wouldn't even start in other languages.
 Introspection. Write a C program that interactively tells you what
 functions it contains.
 And, as you're interested in alternatives to expr, here's my unknown
 proc:

 if ![info proc _unknown] {rename unknown _unknown} ;# keep the original
 proc unknown {args} {
     if [regexp (.+):$ [lindex $args 0] -> name] {
     set args [lreplace $args 0 0 $name =]
     } ;# allow REBOL-style assignments (foo: bar; bar: 17+4)
     if {[lindex $args 1]=="="} {
     # maybe an assignment like "x = 3+4" ? (Blanks matter!)
     upvar [lindex $args 0] _x
     set rest [lrange $args 2 end]
     if [llength [info commands [lindex $args 2]]] {
         return [set _x [uplevel eval $rest]]
     }
     set _x $rest                ;# this should always work...
     catch {set _x [expr $rest]} ;# ...but maybe expr is happy
     return $_x
     } elseif {[regexp {^([^ ]+)\+\+$} $args -> vname]} {
     uplevel [list incr $vname]  ;# allow things like "i++" ...
     } elseif {[regexp {^([^ ]+)--$} $args -> vname]} {
     uplevel [list incr $vname -1]          ;# ... or "j--"
     } elseif {[regexp {^[-+/\*\.0-9 ()]+$} $args]} {
     return [expr $args]         ;# pure expression? "(17+4)/3"
     } else {eval _unknown $args}    ;# let old "unknown" do it
 }
 For calls like
 v = info tclversion ;# maybe assign a proc result (no []!!)
 8.1
 s = this is a string ;# default: shrink-wrapped string (no ""!)
 this is a string
 j = sqrt(2)*3        ;# if expr agrees, the result (no [expr..]!)
 4.24264068712

 Yes, this is still Tcl, and no, it's not like in the book.

 --
 Schoene Gruesse/best regards, Richard Suchenwirth -- tel. +49-7531-86
 2703
 > RC DT2, Siemens Electrocom GmbH, Buecklestr. 1-5, D-78467 Konstanz, Germany
 > My opinions were not necessarily, or will not necessarily be, mine.